In a mobile communication system of an EPS (Evolved Packet System) type specified in 3GPP, there is proposed an operation to be carried out when a P-GW (Packet Data Network-Gateway, packet data network gateway apparatus) #1 receives user data whose destination is a UE (User Equipment) in an idle state under control of an MME (Mobility Management Entity, mobile management node) #1, after the MME#1 which has been suspended due to a failure or the like is restarted.
The operation will be described below with reference to FIG. 7.
As shown in FIG. 7, when the MME#1 is restarted in step S101 in a state (first state) in which a PDN connection #1 including one or more EPS bearers #1 is set among the UE, an S-GW (Serving Gateway, serving gateway apparatus) #1, and the P-GW#1, the state transitions to a state (second state) in which the PDN connection #1 is released between the UE and the S-GW#1 and the PDN connection #1 is maintained only between the S-GW#1 and the P-GW#1.
In step S102, upon receiving user data whose destination is the UE from an external network, the P-GW#1 transmits the user data whose destination is the UE to the S-GW#1 in step S103.
In step S104, the S-GW#1 transmits “DDN (Downlink Data Notification, downlink notification signal)” to the MME#1, because the PDN connection #1 is released between the UE and the S-GW#1.
In step S105, upon receiving the “DDN”, the MME#1 transmits “Paging” whose destination is the UE specified by “IMSI (International Mobile Subscriber Identity)” included in the “DDN”.
In step S106, upon receiving the “Paging” whose destination is the UE, the UE transmits “Attach Request (attach request signal)” to a core network so as to start re-attach processing. The “Attach Request” is transferred to an MME#2 via a radio access network.
In step S107, the MME#2 performs location registration processing for the UE with an HSS (Home Subscriber Server, subscriber information server apparatus).
In step S108, a PDN connection #2 including one or more EPS bearers #2 is set among the UE, an S-GW#2, and a P-GW#2.
In step S109, the MME#2 transmits “Attach Accept” to the UE.